In a wireless LAN realized by a base station and terminals, there is a demand for a minimized power consumption of the terminal.
In a certain kind of wireless LAN, the base station transmits beacon signals periodically to the terminal to notify the terminal of information on identification of the terminal, the presence or absence of data to be transmitted to that terminal, and when a subsequent beacon signal is to be transmitted, all of which are contained in the beacon signal. Therefore, the terminal must constantly receive the beacon signals.
By the way, in the case where an application operated by the terminal application is, for example, an e-mail reception software, and the terminal accesses to a mail server once every one minute to check whether or not any e-mail message has been received, it is a waste for the terminal to turn on its communication terminal every 100 msec at which the beacon signal is transmitted. Further, the wireless LAN is not necessarily limited to include a plurality of terminals, and the wireless LAN can be often realized by one base station and one terminal. In this case, the beacon signal including information of “NO” data to be transmitted to the terminal is received by the terminal every 100 msec, which is a power-wasting operation for the terminal.
What is known for solving such a problem is a technique that the base station extends a period between transmissions of beacon signals. For example, the patent publication 1 (Japanese Laid-Open Patent Application No. 1997/162798 (Tokukaihei 9-162798; published on Jun. 20, 1997)) discloses a technique that the base station changes an interval between transmissions of beacon signals in accordance with the amount of data transmitted to the terminal, and a beacon signal reception timing for the terminal entering a power-on state is changed in accordance with an interval at which the base station transmits the beacon signal. In addition, the patent publication 2 (Japanese Laid-Open Patent Application No. 2003/124940 (Tokukai 2003-124940; published on Apr. 25, 2003)) discloses a technique that the base station determines a polling interval period associated with an amount-of-data range, in accordance with data received over an external network, so that a polling interval period becomes shorter as the amount-of-data range increases.
Also, the terminal realizes such a technique that the terminal checks the beacon signal and if there is no data addressed to the terminal itself, the terminal maintains a low-power consumption mode until the next beacon signal is received, as power save mode of IEEE802.11.
However, the foregoing background art has the following problems. In the technique of the patent publication 1, in the case where the terminal is in a standby state during execution of an IP (Internet Protocol) phone application, an interval between transmissions of beacon signals becomes long since there is no data to be transmitted to the terminal. This makes it impossible to notify to the terminal that telephone incoming call data has been received, if timing is off, upon receiving the incoming telephone call data. Similarly in the technique of the patent publication 2, the base station changes the polling interval after data reception over the external network. This makes it impossible to respond to the demand for a response in real time, if timing is off.
Further, streaming, conversation with IP phone, and other operations are always carried out in a communication state. Therefore, in spite of the presence of periods during which no communications are carried out, it was impossible to suppress a consumed power by performing an intermittent data reception.
Further, patent publication 3 (Japanese Laid-Open Patent Application No. 2004/128949 (Tokukai 2004-128949; published on Apr. 22, 2004)) discloses a wireless terminal and a wireless communication system using the wireless terminal, of which object is to realize decrease of packet delay and improvement in communication quality of an application that requires power saving and a response in real time in voice communications and the like communications, by a wireless terminal varying an interval of intermittent reception for power saving depending on an operation mode of the application, and by transmitting polling data to a wireless base station and data, with respect to the polling data, transmitted from the wireless base station to the wireless terminal in such a manner that they are assigned priorities to depending on an operation mode of the application.
Incidentally, the following will describe differences between the technique in the patent publication 3 and the present invention.
In the technique of the patent publication 3, a setting change is performed only in a terminal, not in a base station. More specifically, in the technique of the patent publication 3, a beacon transmission interval of the base station is not changed. Therefore, the occurrence of delay causes degradation in voice quality since, for example, for the execution of VoIP (voice over IP) when a default beacon transmission interval in the base station is 100 msec, wherein a packetization period of G.711, a typical audio codec of a currently available VoIP, is 20 msec, if this execution is performed with an intermittent reception operation, voice data which is supposed to be transmitted at an interval of 20 msec is received at an interval of 100 msec. In other words, in the technique of the patent publication 3, an application that requires a shorter period than the default beacon transmission interval in the base station cannot be executed with intermittent reception. On the contrary, in the present invention, the base station also sets the beacon transmission period suitably in accordance with a type of application and/or communication property (communication pattern), so that an application that requires a shorter period can be executed with intermittent reception without degradation in communication quality.
In the technique of the patent publication 3, a setting change is not carried out in accordance with a status of an application. More specifically, in the technique of the patent publication 3, there is no difference in intermittent reception interval between a stand-by state and a call state under execution of the VoIP, and in the Embodiment, in the case of the VoIP, intermittent reception is operated by one TIM (Traffic Indication Map). This means consumption of an unnecessary power in the stand-by state. Note that, the TIM is an information element included in a beacon signal for the base station notifying to the terminal during power saving that data addressed to the terminal is stored in a buffer of the base station. On the contrary, in the present invention, the terminal suitably sets a beacon reception period in accordance with the status of an application, so that the beacon reception period is changed between the stand-by state and the call state of the VoIP, and power consumption can be further reduced in the stand-by state.
In the technique of the patent publication 3, a setting range of the intermittent reception interval is determined by DTIM (Delivery Traffic Indication Map). More specifically, in the technique of the patent publication 3, a setting range of the intermittent reception interval is a beacon interval including the TIM at the shortest, and a beacon interval including the DTIM at the longest. A setting of the beacon interval including the DTIM is carried out in the base station. For example, when the base station sets the beacon transmission interval to 100 msec, which is equal to the default beacon transmission interval containing the beacon interval including the DTIM, the terminal cannot change its intermittent reception interval from 100 msec to other value. Note that, the DTIM is TIM included in a beacon signal transmitted at a timing when a TSF (Timing Synchronization Function) timer for synchronization between the base station and the terminal becomes 0. Broadcast data and multicast buffered in the base station are transmitted immediately after the beacon signal including the DTIM. On the contrary, in the present invention, the intermittent reception interval can be set regardless of DTIM, so that power consumption can be further reduced.